1. Field of the Invention
The present invention relates to the hydrocarbonylation and/or carbonylation of alkyl carboxylates, in particular methyl carboxylates and alkyl acetates, in the presence of water. The subject process is, moreover, conveniently represented by the following equation: EQU R--CO--O--R'+CO+H.sub.2 .fwdarw.R'--CO--O--CH.sub.2 --R', R--CO--O--CH.sub.2 --R', R'--CH.sub.2 --OH, R'--CHO, R--CO--OH, R'--CO--OH. (1)
in which R represents a linear or branched chain alkyl radical having from 1 to 16 carbon atoms, a cycloalkyl radical having from 3 to 6 carbon atoms, a phenyl radical (C.sub.6 H.sub.5 --), a radical C.sub.6 H.sub.5 --C.sub.x H.sub.2x -- or a radical C.sub.x H.sub.2x+1 --C.sub.6 H.sub.4 --, with x being an integer ranging from 1 to 6 (1.ltoreq.x.ltoreq.6), and R' represents a linear or branched chain alkyl radical having from 1 to 5 carbon atoms or a radical C.sub.6 H.sub.5 --C.sub.x H.sub.2x --, with x being as above defined, it also being possible for R and R' to be identical.
The process according to this invention is admirably suited to the preparation of one or more of the compounds acetaldehyde, acetic acid, ethanol and ethyl acetate, from methyl carboxylates, and especially from methyl acetate.
2. Description of the Prior Art
Certain authors (compare Journal of the American Chemical Society, 100:19, 1978, pages 6,238-6,239) have reported that it is possible to prepare, in particular, ethyl acetate by the hydrocarbonylation of methyl acetate in the simultaneous presence of ruthenium, an iodine-containing promoter and a proton donor (which is either the HI initially employed in the reaction, or formed in situ from CH.sub.3 I, or a carboxylic acid).
However, the industrial-scale development of a technique of this type, the value of which is not contested in principle, is markedly compromised by the low activity of the catalyst system used.
It has recently been proposed (compare French Patent Application No. 78/20,843) to carry out such reaction in the presence of a cobalt salt and iodine. However, the high pressures required for the catalyst system to develop an acceptable activity hardly make it possible to envisage industrial development of such a process.
Parallel to this, examination of the specialized literature reveals that numerous attempts to hydrocarbonylate methanol in order to selectively obtain either acetaldehyde or ethanol have not resulted in satisfactory solutions. A survey of the various techniques proposed for this purpose can be found, for example, in the introductory portion of U.S. Pat. No. 4,133,966.
It is clearly apparent from this analysis that it would be desirable to have available an efficient process which makes it possible, if appropriate, to prepare aldehydes, carboxylic acids, "homologous" alcohols and, more particularly, alkyl carboxylates from their lower homologs. The term "homologous alcohol" is to be understood as connoting the alcohol R'--CH.sub.2 --OH shown in equation (1) above, which thus contains one carbon atom more than the alcohol (R'--OH) from which the starting ester is derived. A first category of alkyl carboxylates which can be obtained according to the present invention is represented by the formula R--CO--O--CH.sub.2 --R' in equation (1) above. This type of ester contains one carbon atom more than the starting ester and can thus be considered as a "higher homolog" of the starting ester. To simplify the account below, the alkyl carboxylates of the formula R'--CO--O--CH.sub.2 --R' shown in equation (1) above will also be referred to as "homologous esters".